BANDED SOLIDIFICATION MICROSTRUCTURES

Banded microstructures are composed of alternate structures or phases which develop mostly parallel to the transformation front. At low grow th velocities, bands of the same microstructure but with different sca les form through periodic fluctuations of the solidification system. O n the other hand, banding can occur as a transformation microstructure when the growth front becomes unstable to oscillations. This instabil ity is either due, at low velocities, to nucleation of another phase ( peritectics) or, at high velocities, to nonequilibrium effects at the interface which lead to periodic changes of the microstructure. In thi s article, the inherent banded patterns of low velocity peritectic sol idification and high velocity nonequilibrium solidification will be pr esented and their origin will be discussed.